HUNTSVILLE, Texas (AP) — The nation’s most active death penalty state says it won’t change its execution drug, but won’t say how it will replace its supply that expires this month.

“We have not changed our current execution protocol and have no immediate plans to do so,” Texas Department of Criminal Justice spokesman Jason Clark said in a statement to The Associated Press on Thursday, shortly before the state carried out its 12th execution this year. He would not elaborate on how the state will obtain the drug.

Texas switched to a lethal, single dose of the sedative pentobarbital last year after one of the drugs used in its previous three-drug execution process became difficult to obtain and the state’s supply expired. Other death-penalty states have encountered similar problems after some drug suppliers barred the drugs’ use for executions or have refused, under pressure from death-penalty opponents, to sell or manufacture drugs for use in executions.

In the past two years, pentobarbital has been used alone or in concert with other drugs in all executions in the U.S.

Some death penalty states, including Georgia, have said they’re turning to compounding pharmacies for pentobarbital. Such pharmacies make customized drugs not scrutinized by the Federal Drug Administration. It’s hard to tell exactly how many states have used or are planning to use compounding pharmacies for execution drugs because states frequently resist disclosing the source of the drugs.

Missouri, meanwhile, is planning to use propofol, an anesthetic which gained infamy in the 2009 death of pop star Michael Jackson, as the lethal drug for scheduled executions of two convicted killers later this year.

If Texas plans to continue using the same execution drug, it would make sense that it would get it from a compounding pharmacy, said Richard Dieter, executive director of the Death Penalty Information Center in Washington.

“States are taking different routes, but they’re all facing this kind of crisis,” he said.

Dieter said it’s hard to know if getting execution drugs through compounding pharmacies will become the norm for states. But he expects there will be legal challenges to the procedure as inmates and their attorneys will want to find out information about the drug, its dosage, the reliability of its manufacturer.

Georgia’s first use of an execution drug obtained through a compounding pharmacy was put on hold in July after the condemned inmate challenged a new state law that bars the release of information about where Georgia obtains its execution drug.

“This is a basic matter of due process. A defendant has a legitimate interest in how he’s going to be executed,” he said.

The FDA considers compounding pharmacy products unapproved drugs and does not verify their safety or effectiveness. However, such businesses have come under scrutiny after a deadly meningitis outbreak was linked to contaminated injections made by a Massachusetts compounding pharmacy.

As of May 2012, Texas had 46 of the 2.5-gram vials of pentobarbital — presumably enough to execute as many as 23 prisoners, since each execution requires a 5-gram dose. The execution Thursday of Robert Gene Garza, convicted of being involved in the fatal ambush shootings of four women in the Rio Grande Valley, was the 21st lethal injection since that disclosure.

Texas by far has executed more inmates than any other U.S. state since a Supreme Court ruling in 1976 allowed executions to resume. Since 1982, when Texas resumed carrying out capital punishment, the state has executed 503 inmates.

It’s possible the drug issue could result in court challenges by death penalty opponents or attorneys for the inmates facing imminent execution, such as Arturo Diaz, set to die in Texas next week for the slaying of a Rio Grande Valley man stabbed nearly 100 times during a 1999 robbery.

Garza, in late appeals Thursday to the U.S. Supreme Court, contended the state should disclose the expiration date of drugs intended for his execution, arguing that those nearing the end of their shelf life could fail and leave him in pain, paralyzed or comatose.